A lithography apparatus is a machine that applies a desired pattern onto a substrate, usually onto a target portion of the substrate. A lithography apparatus can be used, for example, in the manufacture of integrated circuits (ICs).
In the semiconductor industry there is a strong pressure to increase the density of devices, e.g. transistors, in an integrated circuit that can be formed on a substrate. To achieve increased densities, the accuracy and precision of lithography apparatuses and processes must be improved. For example, to form a device it is generally necessary to successively apply several patterns to a substrate with very high accuracy of placement. The placement error between patterns is known as overlay and the maximum allowed overlay might be only a few nanometers, especially for layers which must be formed with multiple patterning steps.
Within a lithography apparatus there are various components whose physical size or shape directly or indirectly affects the accuracy of the devices formed thereby. Examples include: a substrate table that holds the substrate to which a pattern is applied; and a reflector in a projection system. To maintain these and other components at their nominal sizes and/or shapes it is common to provide temperature control systems to maintain components at a specific temperature. Also, one component, e.g. a substrate table, may be maintained at a constant temperature in order to influence the temperature of another component, e.g. a substrate, which cannot itself be provided with a temperature control system. However, improvements in this regard are desirable.